1. Field of the Invention
The present invention relates to a reference current generating circuit, and more particularly, to a reference current generating circuit having a constant output level regardless of a temperature variation.
2. Description of the Related Art
In general, a reference current generating circuit is built in most of integrated circuits for communication, and considered as a very important circuit used as a current source of an essential electronic circuitry.
Similarly to typical integrated circuits, a reference current generating circuit accompanies an output level fluctuation inevitably due to a variation in temperature and process. Unlike other circuits in the integrated circuit, however, a reference current variation may have an adverse effect on other circuits because the reference current generating circuit is used as a current source of other circuits. Therefore, the reference current generating circuit should be insensitive to the effects resulting from external conditions such as a temperature variation.
A related art reference current generating circuit generates a constant current by applying a reference voltage, which has a constant level regardless of a temperature variation, to a resistor. Here, the reference voltage is output from a constant voltage source (e.g., bandgap reference circuit) that generates a constant voltage regardless of the temperature variation. To generate a current having a constant level regardless of the temperature variation in the related art reference current generating circuit, it is very important to maintain the resistance of the resistor constantly. Meanwhile, a resistor integrated through CMOS process, for example, an n-well resistor or a polysilicon resistor, has a resistance that is very sensitively changed as a temperature varies. Accordingly, the related art reference current generating circuit cannot use the n-well resistor or the polysilicon resistor that is sensitive to the temperature variation, and thus employs an external resistor capable of adjusting the resistance to thereby generate the reference current. This makes it difficult to achieve a high integration of a circuitry after all.